Wireless devices or terminals for communication are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server, such as server providing video streaming service, via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, computers, or tablets with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
A cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. The base stations and wireless devices involved in communication may also be referred to as transmitter-receiver pairs, where the respective transmitter and receiver in a pair may refer to a base station or a wireless device, depending on the direction of the communication. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to a wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for communication with terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE is controlled by the radio base station.
An uplink multiple access scheme for LTE is Single Carrier Frequency Division Multiple Access (SC-FDMA), also known as Discrete Fourier Transform (DFT) Spread-Orthogonal Frequency Division Multiplexing (S-OFDM), where assigned Resource Blocks (RBs) should be contiguous in the frequency domain. SC-FDMA has a significantly lower Peak-to-Average-Power-Ratio (PAPR), also known as Cubic Metric (CM), and therefore avoids excessive cost of transmitters in UEs. Further enhancements for non-contiguous resource allocation in the uplink have been introduced in LTE-Advanced. Contiguous resource allocation means that the allocated resource blocks are contiguous in the frequency domain, whereas non-contiguous resource allocation means that the allocated resource blocks are not contiguous in the frequency domain. When using clustered DFT-S-OFDM with a maximum of two clusters, Physical Uplink Shared Channel (PUSCH) transmission on two separate contiguous sets of RBs within a single component carrier can be supported. Cluster is defined herein as a group of contiguous resource blocks. Clustered DFT-S-OFDM uses a single DFT operation as SC-FDMA and changes a resource element mapping at an output of DFT from a single cluster to a multiple clusters of subcarriers. This results in that the resulting waveform is no longer ‘single-carrier’ but still has a low PAPR or CM. Such dual-clustered PUSCH transmission increases the flexibility of uplink resource allocation and thus can maximize the utilization of the spectrum.
On the other hand, Link Adaptation (LA) and Hybrid Automatic Repeat reQuest (HARQ) are two features that enable efficient and robust data transmission in wireless communication systems. With LA, a transport formats such as e.g. a Modulation and Coding Scheme (MCS) can be adapted to current channel conditions. For instance, when a UE experiences poor radio conditions, it can use a low order MCS, e.g. Quadrature Phase Shift Keying (QPSK) with coding rate 1/6, to achieve robustness against the noise and the channel fades, whereas with a highly reliable channel, the UE may use high order MCSs, such as e.g. 64-Quadrature Amplitude Modulator (QAM) with coding rate 5/6, to improve its throughput. Coding rate 1/6 and 5/6 here mean the ratio between the information bits and the physical channel bits, which are the actual bits transmitted via the physical channel and include the information and also the redundancy used for error correction. Higher coding rate means less redundancy and thus higher spectrum efficiency. In uplink, the eNodeB needs to estimate the Signal-to-Interference-plus-Noise Ratio (SINR) of UEs according to a previously received PUSCH message or Sounding Reference Signal (SRS). The eNodeB then selects the MCS leading to higher expected throughput with respect to a predefined BLock Error Rate (BLER) target, typically set as 10 percent in LTE. An index of the selected MCS is then sent back to UEs via uplink grants in PDCCH. With HARQ, a Cyclic Redundancy Code (CRC) is appended to the information bits of each code word. Code word may be seen as a group of bits that should be transmitted and decoded together. It comprises the information bits and an CRC. The CRC is an error-detecting code that is used for determining if the code word can be correctly decoded. and used to check if the transmission is successful. In case of correct detection which means the CRC is ok, i.e. the code word is correctly decoded, an Acknowledgment (ACK) message is sent to the UE; otherwise, a Negative ACK (NACK) message is sent to the UE, and the UE has to retransmit the code word.
CRC for uplink transmissions can be used to control LA margin to compensate for systematic errors in SINR estimation for link adaptation. The process is also referred to as an outer loop gain adjustment. With outer loop gain adjustment, link adaptation becomes more aggressive, i.e. the LA chooses higher modulation order and/or coding rate and may get higher Block Error Rate (BLER) than the target one, when a CRC is ok and more defensive when a CRC is not ok.
With the support of clustered DFT-S-OFDM, an uplink scheduler in an eNodeB may dynamically assign contiguous or non-contiguous RBs, i.e. two clusters of RBs, to UEs based on their buffer requirements, channel quality measurements and scheduling strategies. The estimated SINR is an important input for Link Adaptation. The problem in this case is that the estimated SINR is inaccurate. If the accuracy on SINR estimation is lost, the Link Adaptation function will choose an improper MCS based on the estimated SINR, which further may results in higher block error rate or less throughput.